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Not fully understanding Grounds

  1. Jul 19, 2012 #1
    I'm a total electronics noob. I've taught myself programming and many skills and i've always wanted to learn how to build circuits and understand electronics. I've begun learning/researching various topics recently and one thing i can never comfortably understand is grounding.

    So, i prepared this nooby diagram, and know it'll be trivial for someone with a better understanding of all this to help me out:

    https://dl.dropbox.com/u/1010927/circuit.png [Broken]

    Would it work something like A? like B? neither? completely off base and something like A is impossible? etc. I have no background so straight forward diagrams like this are all i can understand at the moment.

    much appreciation to those who answer :)
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jul 19, 2012 #2
    Diagram A is fine. In Diagram B, the voltage on the terminals of the battery are a bit awkward. You see how there is a straight path from the negative terminal of the battery to ground with no other components in the way? This means the voltage there is 0 V, just like in Diagram A (there is a clear path from negative terminal of battery to ground). Since the battery is 1 V, jumping from the negative terminal up to the positive terminal is a change of 1 V (since it's a 1 V battery), so the voltage on the positive terminal is 1 V. So you see, Diagram A and Diagram B are actually the same thing. Ground is the same everywhere in the circuit. You can have each individual component have their own wire to ground as in Diagram A, or you can connect the components together and wire the combination to ground as in Diagram B. Usually, people do what makes their diagrams look clean and easy to read. Hope this helps, let me know if you have any other questions.

    EDIT:
    I don't have my usual circuit simulator on me, but I used this Java applet to create a circuit and simulate it (see attachment). Note current is traveling clockwise, and is the same everywhere in each circuit.
     

    Attached Files:

    Last edited: Jul 19, 2012
  4. Jul 19, 2012 #3
    thanks for the response!

    so to be clear, if i were to stick the negative terminal of a battery into the ground, like physically THE ground with a metal spike, and then run a wire to a light bulb from the positive terminal, and then the other pole of the light-bulb into THE ground with a spike once again, the light would turn on? seems a little strange cause then couldn't power companies send ONE line to us, and we just use the ground as the other "terminal" of an outlet? is this how they do it? why do outlets have 3 terminals? I always thought you needed a closed loop and this is why grounds have seemed pretty enigmatic to me so far.
     
  5. Jul 19, 2012 #4
    Yes. Remember, ground is the same everywhere, so, in a sense, you are completing the loop. You began at ground, you ended at ground.

    I'm not exactly sure what you mean here. Yes, power plants only send electricity to us, we do not send any energy back to power plants to "complete the circuit." We complete the circuit at home by grounding the wire. If you want to know why there are multiple lines, let me warn you, this is a much more advanced topic, so I've thrown it under a spoiler tag, but feel free to read if you're interested.

    Power companies send multiple lines because they are transmitting via Alternating Current (AC). A wire contains resistance, so transmitting over long distances can decrease the amount of power sent, because energy must be expended to push through the wire's resistance. In AC circuits, power is a complex number, it has a real and imaginary component. When you transmit across one line, you get some real and some imaginary power at the receiver. Imaginary power is useless, we want real power. It turns out that transmitting across multiple lines allows you to shift imaginary power into real power, therefore transmitting more power that can be used by the receiver.

    I actually never really thought about this, so I looked it up here. Apparently, the third prong (the round hole) is used to ground the covering of an appliance. Let's say a wire touches a metal case and then you touch the case, you complete the circuit because electricity flows from the outlet to the case, into you, and then into ground. Instead, give the case a direct path to ground through the third prong, that way current can flow directly to ground instead of through you to ground, even when you touch it.

    You do. Always. However, what you need to realize about ground is that ground is the same everywhere. In a sense, ground is a wire that is easily accessible everywhere. Remember, Diagram A and Diagram B are the same exact diagrams, even though one has two grounds in it. You can combine the two grounds together, and therefore you have a closed loop. Keep the questions coming if it's not clear.
     
  6. Jul 19, 2012 #5

    jim hardy

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    You're hardly alone many people don't understand it. Somehow they think ground is an absolute of some sort, like absolute zero temperature or absolute zero pressure , that 'sucks up' electricity.

    Ground is just another wire, as Gordon said... But it goes most everywhere. I like the British term for it, "earth", much better.
    So we often connect the negative lead of our voltmeter there and express voltage with respect to it.

    But what if you're in an airplane? or in a lunar capsule on the moon?

    What is the voltage between earth and moon?

    What is your concept of "ground"?

    It will help you to take time now to flush out those misconceptions about ground.
    Current wont flow there unless ground is on the current's way back where it came from.
    You can demonstrate that with a simple flashlight, get one with a metal case and connect your meter set for milliamps between flashlight and a water pipe..
    Your fig B is mighty close to that just put a meter in the wire to earth. Do it for real if it seems confusing.
    Observe that in your figure A, the current must flow through earth to get back to the battery from whence it came. But not in your fig B.

    The humble flashlight has a lot to teach us if we'll just look.

    old jim
     
    Last edited: Jul 19, 2012
  7. Jul 19, 2012 #6
    Very impressed with the responses, thank you very much guys!

    I think it's pretty clear to me now, aside from the fact that when i tried *A* it didn't work (although my set up was less than ideal). i had just used a short nail stuck into the soil but i'm guessing you need a pretty dug in. high area contact with the ground to overcome the insulation of soil/moisture/etc. like the coil of wire they bury near power lines or a copper water pipe. It's pretty clear now!

    This also helped me confirm those thoughts:
    http://en.wikipedia.org/wiki/Single-wire_earth_return

    My concept of ground would basically be, some 0v area/conductor!
     
    Last edited: Jul 19, 2012
  8. Jul 20, 2012 #7
  9. Jul 22, 2012 #8

    Integral

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    I disagree with Gordon concerning your drawings, as you found A is not guarenteed to work at all. If the ground were saturated with water it would do best. A stake driven into the ground is not supposed to carry current, it is for potential reference alone.

    Drawing B is fine, will always work, it just sets a reference point having no real effect on the circiut.
     
  10. Jul 23, 2012 #9

    psparky

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    I agree with "Integral", Earth can be a reasonable conductor....but it certainly does add extra resistance. And like he said....not cool to run current thru the earth......I would not run a circuit like figure A

    Figure B is fine and it sorta represents the electrical panel in your home....in other words, neutral is tied to ground and then earthed.

    And yes.....almost no one understands grounding all the way. All seems to be kind of a mystery at work. We do our best, but there is always a bit of guessing with ground mats and ties and all that fun stuff. Ways to ground things differ from "expert" to "expert".....and the code book is confusing as always.

    Figure A and B would both technically work.....but Figure A light is going to be dimmer than Figure B light. You are simply burning watts in the earth......heating the ground if you will.
     
  11. Jul 23, 2012 #10

    jim hardy

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    indeed dirt is not so good a conductor as copper.

    When earth is asked to carry substantial current it exhibits a voltage drop, just as would any real (non-super) conductor.

    In substation design they design the earthing system such that under a fault, the voltage drop per yard, which is about a man's stride, isn't enough to electocute him.

    Now think about what happens when a lightning bolt strikes the ground, or a tree or power pole.
    At the bottom of the lightning bolt the potential is quite high as the current flows away from it, V=IR,
    and becomes lower at increasing distance;
    probably lines of equal potential would approximate circles centered on the strike.

    This was vividly demonstrated to me one day when lightning struck the power pole outside my house.
    At that instant I was using my new Craftsman drill, a metal cased one, and the third prong tied its case to the green grounding wire in my electrics which goes out to the copper earthing wire on utility pole.
    So i was briefly holding in my hands a metal drill connected by copper wire directly to the bottom end of a lightning bolt.
    Good thing i was wearing thick soled shoes.... a lightning bolt lasts long enough for you to holler "Gaaahhh" and throw the drill.

    i think i might have told that story last year someplace - sorry, old men repeat themselves. repeat themselves. repeat themselves..........

    old jim
     
    Last edited: Jul 23, 2012
  12. Jul 23, 2012 #11

    psparky

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    BTW....to Quazi, no one in there right mind would ground a 1 volt battery powering a light! The circuit obviously runs fine without the ground in figure B.

    Grounding higher voltages is 100% the way to go....but something this simple....not so much.

    One further thought.....the 12 volt battery system in your car....the negative terminal is connected to the steel frame of the car and the motor. All the electric devices travel through the steel frame of the car and motor. The steel acts as the ground. Steel has very little resistance just like a good copper conductor. The massive positive red terminal cable goes directly to the starter motor (draws huge amps compared to everything else) The smaller wires from the positive terminal power everything else.
    This is clearly a different type of ground than "Earth". Nothing touches the earth on your car except your tires which are very insulated from electricity.
     
    Last edited: Jul 23, 2012
  13. Jul 23, 2012 #12

    sophiecentaur

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    If you can make a good contact (at each end of the ground portion of yur circuit, over a large area, with a thick copper spike or even a network / mesh of copper wires all over a wet ground then it will work as well as a nice piece of copper joining the two ground connections. The problem is that you can't rely on a good ground ('earth') connection (particularly one that someone else says they installed). Places where a 'ground return' is often used are where you have a good metal framework or shell - as in a car - but they can let you down through corrosion at bodywork joints and many car electrics nowadays use explicit 0V return cables - because more an more bits tend to be made out of plastic, these days.

    I shouldn't lose too much sleep about the mystical bits in that 'hidden spoiler' unless you want to get into three phase distribution. Ordinary, two wire AC has some advantages over DC distribution in that that you can transform up to high voltages and reduce the losses due to the current flowing through the resistance of the cables. However, there are other losses due to Capacitance of cables and the Inductance of some loads so it can cause a lot of problems. Long or international links tend to use DC (e.g. under the English Channel) to great advantage.
     
  14. Jul 23, 2012 #13

    psparky

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    Look at me and Sophie thinking alike....I'll be a son of a gun....blush:)
     
  15. Jul 23, 2012 #14

    sophiecentaur

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    You're obviously winning me over!
     
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